Multilayer bearing having a base of steel and a surface layer of a lead alloy



R. -J. M DONALD ET AL MULTILAYER BEARING HAVING A BASE OF STEEL ANDSept. 24, 1968 $22.4 omhuwJw E v N \\\N NdE A SURFACE LAYER OF A LEADALLOY Filed Feb. 14, 1966 wzzzmOu INVENTORS ROBERT J.M0cDONALD JAMES F.WARD ATTORNEY MULTILAYER BEARING HAVING A BASE OF STEEL AND A SURFACELAYER OF A LEAD ALLOY Robert J. MacDonald, Moreland Hills, and James F.

Ward, Cleveland, Ohio, assignors to Clevite Corporation, a corporationof Ohio Filed Feb. 14, 1966, Ser. No. 527,130 8 Claims. (Cl. 29-1835)ABSTRACT OF THE DISCLOSURE A multilayer bearing comprising a steelbacking member bonded to a surface layer of lead alloy containing tinand copper through means of intermediate layers. One of the intermediatelayers is composed of silver or copper and a minor amount of lead oxideor silicon oxide.

This invention relates generally to an improved bearing and moreparticularly to a bearing having a surface layer of relatively corrosionresistant material and an intermediate layer providing high fatiguestrength.

The bearing herein under consideration is adapted to be employed for usein applications where high load and/ or corrosion conditions arenormally encountered. In bearings of this type it is generally requiredto provide a surface layer which has a fairly high lead-tin content. Alayer composed of such a material will inhibit corrosion and aid inpermitting the bearing surface to adjust to misalignment and shaftsurface conditions. A variety of surface layer materials for suchbearings are known. It has also been customary in the prior art tocombine in such a bearing an intermediate layer of leaded-bronze oraluminum-tin alloys. The prime objective of such a layer has been to addfatigue resistance to the bearing member. However, experience has shownthat leadedbronze, while providing good fatigue resistance, is subjectto attack by acid products found normally in lubricants which havedeteriorated due to heat, oxidation, as Well as moisture. The acidiccontaminants also attack the lead phase of the leaded-bronze bearingsurface after the above mentioned surface layer, or overlay, has beenworn away. The removal of the lead phase weakens the bearing structureand accelerates its failure. The tendency for seizure increases inalmost direct proportion as the lead is removed by the forces ofcorrosion. While an intermediate layer composed of aluminum alloys andincluding, for example, 5 to 7 weight percent tin, exhibits goodcorrosion resistance, the generally poor fatigue resistance of thismaterial limits its use in any high load application.

The bearing in accordance with this invention avoids these disadvantagesby establishing a strong substrate to provide high fatigue strength andcorrosion resistance while allowing a sufficient degree ofconformability to adjust to misalignment conditions that may occurduring the life of the hearing. The advance in this art has been madepossible by creating a substrate which provides the required propertiesand by placing the same into a compatible environment.

The invention takes advantage of several properties of lead silicate toproduce an intermediate layer with good fatigue and corrosionresistance. These properties are embodied in a composition which ispredominantly composed of copper or silver and includes a lead oxidebase additive containing a certain percentage of silicon oxide. Whilethis composition, per se, is not new, it has been found that suitablebearings for high load conditions could not be achieved withoutovercoming innumerable problems which stood in the way of providing acoherent bearing structure exhibiting all of these advantages nitedStates Patent 0 of the individual materials. The difficultiesencountered in providing such a coherent structure will be pointed outin more detail in order to facilitate a better understanding ofapplicants invention and contribution.

A metallurgical system of predominantly copper or silver and a leadoxide base additive does not provide sufficient strength of the degreenormally required for high load bearings. Such a composition will,normally, develop fatigue cracks when operated at 10,000 p.s.i. in theUnder wood Fatigue Test. It will of course be appreciated thatstrengthening mechanisms for such metallurgical systems are verylimited. It has been found that neither solid solution hardening norheat treatment is desirable because of thermodynamic instability of thelead silicate phase at the sintering temperature. Also, normal hardeningconstituents for copper, such as tin, zinc, and nickel may not be usedinasmuch as such material change the free energy relationships betweenthe copper and the lead silicate resulting in the conversion of thelatter to lead. Such conversion is undesirable as the lead silicateprovides the bearing with self-lubricating qualities. In accordance withthis invention it has now been found, that when an intermediate layer ofsuch material is strain hardened the structural characteristics of thelayer may be appreciably improved and the problems associated withfatigue and cracking avoided.

It is therefore the primary object of the invention to provide amultilayer bearing for high load applications which has improved fatigueresistance, conformability and embedability and is substantiallyimpervious to attack by corrosion agents normally found in deterioratedlubricants, and includes an intermediate layer which is adapted to coator establish a film of lubricant upon the shaft surface and to enhancethe wetability of the oil to which the bearing is normally exposed.

It is a further object of this invention to provide a bearing materialhaving high corrosion resistance, but normally insufficient fatiguestrength, for high load hearing use and to make such materialmetallurgically compatible with the surface layer of the bearing.

One aspect of the present invention resides in providing a multilayerhearing which includes a steel backing member coated, byelectro-deposition, with a relatively thin layer of copper. Superimposedupon the copper plated member is a composite layer of strain hardenedmaterial the base of which is selected from a group of metals whichconsist of copper and silver. Added to this base material is apulverized mixture of lead oxide and silicon oxide (lead silicate). Arelatively thin barrier layer resistant to tin diffusion iselectro-deposited upon the composite layer to prevent any diffusion oftin from the surface layer. The surface layer, aside from the tinalready mentioned, contains a small percentage of copper and the balanceis substantially 'all lead.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the followingdescription taken in connection with the accompanying drawings, and itsscope will be pointed out in the appended claims.

In the drawings:

FIG. 1 is a cross sectional view of a typical bearing made in accordancewith this invention; and

FIG. 2 is a diagrammatic illustration of the method for producing thebearing.

Turning now to FIG. 1 there is shown a multi-layer bearing structure 10composed of a conventional steel backing member 12 coated with a thinlayer of copper 14. The copper layer 14 has a thickness between .0002and .0006 inch. The selection of the thickness depends in part upon theparticle size and metallurgical characteristics of the succeeding layerand more particularly, as

hereinafter discussed the lead silicate particles contained therein. Ithas been found that through proper selection and control of the size andamount of the lead silicate, the thickness of the copper layer can beheld down to the .0002 inch minimum. The term lead silicate denotes asystem of lead oxide and silicon oxide. Generally, it may be said that acopper layer thinner than the .0002 inch results in a sharply reducedbond.

In order to provide the bearing with good corrosion resistance as wellas good fatigue resistance, there is provided an intermediate layer 16composed of a matrix material of either copper or silver. The copper orsilver is provided in the form of powder particles which are sinteredtogether with powder particles of a lead oxide and silicon oxideadditive. It should be noted that the presence of the lead oxide phaseis imperative in order to provide the bearing with self-lubricatingcharacteristics. Numerous metallurgical products have the tendency toreduce lead oxide to lead during sintering. It is therefore necessarythat said additive materials be blended only with powder particles of amaterial whose free energy of oxide formation is more positive than leadoxide, or utilized in a system which inherently protects the lead oxidephase. The composite layer 16 is, preferably, composed of 80 to 95weight percent of the aforestated base material and the balance isformed of, essentially, lead oxide and silicon oxide. The amount ofsilicon oxide may be in the range of up to 40 weight percent of theadditive material. The most suitable combination of base and oxideadditive material is approximately 95 weight percent copper, theremaining 5% being constituted of 92% lead oxide and 8% silicon oxide.It should be reiterated at this point that the above mentioned .0002inch layer of copper, see 14, is needed to prevent the lead silicatefrom reacting with the steel at the sintering temperatures to form leadand iron oxides which are detrimental to bond quality.

A layer 18 composed of a material resistant to tin diffusion iselectro-deposited upon the intermediate layer 16. The layer 18constitutes a barrier to tin and is formed of a metal, or metal alloy,such as nickel, iron, cadmium, zinc and cobalt. In the prefer-redembodiment the barrier layer 18- is composed of nickel and has athickness approximately between .00005 and .001 inch.

Finally, the bearing is provided with a surface layer 20 which hasqualities of high fatigue resistance and properties adapted for highsurface speeds and loads. In the preferred embodiment the surface layeris composed of from 6 to 12% tin, 0.5% to 6% copper and the balancelead. The soft lead base permits the absorption of foreign particlesfrom the oil environments and allows adjustment for slight misalignmentbetween the bearing and the journal. The characteristic of embedabilityand corrosion resistance can only be retained as long as the tin isprevented from migrating towards the copper which is contained in layer14 and for which it has a metallurgical affinity. It is for this reasonthat a barrier layer 18 must be interposed between layers 16 and 20.

Particularly useful bearing properties are obtained by forming thesurface layer 20 with a tin content and 3% copper with thebalance'substantially all lead. The thickness of layer is approximatelybetween 0.0005 and 0.004 inch.

Turning now to FIG. 2, there is shown a process diagram for producingthe bearing above described. A steel strip 22 is coated, byelectro-deposition, with a layer of copper and this strip is passedunderneath a hopper 24 containing the powder particles of theintermediate layer 16 and deposits these particles upon the strip 22.With the powder blend spread upon the copper plated steel strip, thelatter is passed through a sintering furnace 26 at 1500 F. To preventoxidation of the copper or a reduction of the lead silicate, it isnecessary to sinter in a dry, inert atmosphere. Pre-purified nitrogenhas been used most successfully for this purpose. The strip is sinteredat the peak temperature for approximately five minutes.

In order to avoid abrasion treatment of the copper plated strip prior tospreading the powder particles, it has been found that the time lagbetween the plating and sintering is critical. An excessive interveningtime lapse will tend to discolor and tarnish the copper anddetrimentally affect the bonding between the steel backing 12 andintermediate layer 16. The abrasion step can be eliminated if and whenthe strip is immediately used after plating and before such oxidationand tarnishing progress begins. Subsequent to sintering, the thicknessof the strip is reduced by passing through a pair of cold rolls 28. Therolling step densifies the sintered layer with an approximate reductionof in the thickness of layer 16 and about 5% in the thickness of thesteel backing 12. After the rolling step is completed the strip isresintered in furnace 30 under the same conditions as outlined withrespect to furnace 26.

As has already been alluded to in the introductory part of thisspecification, it has been vitally important to strengthen thecopper-lead-silicate system in order to improve the hardnesscharacteristics of the layer 16. Experiments have indicated that ahardening of the strip after resintering will appreciably improve suchcharacteristics. The following Table I is indicative of the level ofhardness that can be achieved under indicated conditions.

TABLE I.STRAIN IIARDENIN G Reduction of Layer 1?. Layer 16 layers 12, 14and 1G hardness, RB hardness, BIIN 2 thickness, inch 1 R RockWellhardness B scale. 2 BHNBrinell hardness number.

The strain hardening is accomplished by passing the strip throughsuitable rolls 32 at room temperature. In the preferred embodiment thestrip is strain hardened to effect an increase in the hardness of thelayer 16 to about 90 Brinell Hardness Number. This requires,approximately, a 25% reduction in the layer thickness.

The composite strip 22 is then cut and individual pieces are formed intosuitable bearing shapes. The surface of the resulting bearing shape isfreed of lead silicate particles. The removal of such particles can beaccomplished by a variety of mechanisms. Initially, it should be notedthat it is difiicult, if not impossible, to obtain a suitable bondbetween the intermediate layer 16 and the surface layer 20 withoutremoving such particles. Experiments have shown that the nonconductinglead silicate particles produce weakly adhering layers which have atendency to crack and fail. Inasmuch as only the particles immediatelyat the surface need be removed it is possible to dissolve such leadsilicate particles by exposure to ammonium acetate. A fairly goodadherence between the layer 16 and the electro-deposited nickel can beobtained by such a process. For certain operations the time andtemperature cycles required for such chemical removal are frequentlyundesirable. As an alternative, and under certain conditions, thesurface of the bearing may be mechanically prepared, for instancemachining with a diamond boring tool. With this method a very shallowdepth of the lead silicate removal can be obtained. Vapor blasting canalso be used to remove the lead silicate at the surface.

Each bearing is electroplated with current density of 20 amps per squarefoot for 6 minutes in a Watts nickel bath. Thereafter the surface layer20 is deposited by immersing the bearing in a lead-tin-copper fluoboratebath with current density of 20 amps per square foot for 12 minutes toprovide a minimum thickness of 0.0005 inch.

While there have been described what are at present considered to be thepreferred embodiments of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is aimed,therefore, in the appended claims to cover all such changes andmodifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A multilayer bearing comprising: a steel backing member coated with alayer of copper having a minimum thickness of not substantially lessthan 0.0002 inch; an intermediate layer bonded to the coated backinglayer and composed of approximately 80 to 95 weight percent of a basematerial selected from a group of metals consisting of copper andsilver, and the balance of an additive metal selected from a groupconsisting essentially of lead oxide and silicon oxide; and a relativelythin barrier layer on said intermediate layer of material resistant totin diffusion and selected from a group of metals consisting essentiallyof nickel, iron, cadmium, zinc and cobalt or a combination thereof; anda surface layer bonded to the barrier layer composed predominantly oflead and the balance comprising tin and copper.

2. A multilayer bearing according to claim 1, wherein said copper layeris electro-deposited upon said backing member and has a thickness ofless than .0006 inch.

3. A multilayer bearing according to claim 2, wherein said copper layerhas a thickness ranging between .0002 and .0006 inch.

4. A multilayer bearing according to claim 1, wherein said surface layercontains approximately 10% tin, 3% copper and the balance substantiallyall lead.

5. A multilayer bearing according to claim 4, wherein said surface layerhas a thickness between .0003 and .002 inch.

6. A multilayer bearing according to claim 1, wherein the additivematerials of said intermediate layer consists essentially of 0 to Weightpercent silicon oxide and the balance lead oxide.

7. A multilayer bearing according to claim 1, wherein said intermediatelayer has a thickness between .002 and 0.100 inch.

8. A multilayer bearing accroding to claim 6, wherein said additives arecomposed of approximately 92 weight percent lead oxide and 8 percentsilicon oxide.

References Cited UNITED STATES PATENTS 2,459,172 1/ 1949 Luetkemeyer20196.3 2,635,020 4/1953 Beebe 29196.3 2,970,933 2/1961 Barera 29196.3XR 2,977,673 4/1961 Weinman 29196.3

HYLAND BIZOT, Primary Examiner.

